Knitted spacer structure is a three-dimensional knit structure constructed from a spacer yarn layer formed between the superficial layers of two separate knit structures connected together by means of yarns. There are many varieties of knitted spacer structures and they use a wide range of raw materials enabling easy changes of width, density and interval width. With the combinative application of resin impregnation, surface coating and lamination processes, they obtain wearabilities and mechanical and physical properties such as air permeability, moisture-absorption ability, moisture permeability, shock resistance, filterability, compressive modulus of elasticity, fireproofing and thermal insulating properties, and are thus extensively used in reinforced structures of industrial knitting materials and structural composite materials.
At present, there are three typical knitted spacer structures. The first is the warp-knitted spacer structure knitted on a double needle bed warp knitting machine, and in this fabric structure warp plain stitch can be used for ground stitch, and chain weft inlay stitch and other stitches can also be used. The second is the weft-knitted spacer structure knitted on a flat weft knitting machine, and in this fabric structure tuck stitch is used for yarn connection and rib stitch and other stitches can also be used. These two types of knitted spacer structures differ in ground stitches and the way of connection yarn feeding, while their common disadvantage is that the superficial layers thereof are both yarn loops without any straightened reinforcement yarns fed, and the bent structure of knitted loops hinders the full utilization of the mechanical properties of yarns, thus resulting in the poorer mechanical properties of their superficial structures. The third is the biaxial reinforced weft-knitted spacer structure formed by two biaxial reinforced weft-knitted single-face knitted structures separately knitted by two needle beds and thereafter connected by connection yarns on a flat weft knitting machine, in which case cylindrical or tube-like biaxial weft-knitted spacer structures cannot be formed.